I stumbled on this website a couple days ago while looking for info about proceedural noise generation. The author assumes little to no previous knowledge of shaders and takes you from shading a simple sphere with a solid color through deferred shading, GI, and post effects. They are also text/image based, so you don’t have to constantly be pausing/playing a video. The tutorials are technically unity specific (there are a few Unity macros and libraries used), but it would be trivial to follow along in another engine. Hopefully someone will find this useful.
EDIT: Sorry, I forgot to mention the shader specific tutorials start at section 1.3 Rendering. Here is a direct link to the first tutorial: http://catlikecoding.com/unity/tutorials/rendering/part-1/